Conventional air conditioning system controls temperature and humidity in combination. It realizes the control by changing the temperature and humidity of the air to be output into rooms. However, such system will lead to a poor performance of the cooling unit and a waste of energy grade because it deals with sensible and latent heat in the same time. Besides, such system can result in stagnant water and cause problems such as the propagation of mildew.
There are some relevant solutions available in the art. For example, U.S. Pat. No. 7,721,560 discloses a system for controlling temperature and humidity in an enclosure, that has a central air conditioning system; a dehumidifier attached to a return air duct of the central air conditioning system; and a system control that comprises a thermostat, dehumidstat and can control a cooling solenoid valve to provide temperature control, and control a dehumidifier solenoid valve to provide humidity control. The cooling solenoid valve and the dehumidifier solenoid valve can be independently activated based on the temperature and humidity of the enclosure.
U.S. Pat. No. 5,325,676 discloses s convertible desiccant assisted air pre-conditioner for implemented use to dehumidify an air column delivered into an air conditioned space, and including: a first ducting means dedicated to dehumidification of incoming air at an intake end and delivering supply air at a discharge end for conditioning said air conditioned space, a second ducting means dedicated to desiccant regeneration by means of return air from said air conditioned space, there being at least one air flow control means at an intake end of the second ducting means, a third ducting means for receiving return air at an intake end and delivering exhaust air at a discharge end, there being one air flow control means space at the intake end of the third ducting means and at least one air flow control means space at the discharge end of the third ducting means, a coupler means duct open between the at least one air flow control means at an intake end of the second ducting means and said one flow control means space at the intake end of the third ducting means, desiccant dehumidifying means exposed to an air column flowing through the first ducting means for dehumidification and exposed to an air column flowing through the second ducting means for regeneration of weakened desiccant, heater means for tempering the air column to a regenerating temperature through the second ducting means, and heat transfer means exposed to air columns flowing through each of said first and third ducting means.
However, it costs too much to build a conventional system because several parts need to be designed separately and it is difficult to adopt modular design. In addition, the conventional systems are not energy saving, and particularly they are not efficient in humidity control. Therefore, in an epoch that energy saving is highly advocated, a temperature and humidity independent control air conditioning system with low cost in building and running is expected.